The invention generally relates to imaging systems, and relates in particular to imaging systems that employ an illumination modulator.
Imaging systems such as those disclosed in U.S. Pat. No. 6,433,934, may include an illumination source, a field lens system, an illumination modulator, imaging optics and an imaging surface. During imaging, the field lens system directs the illumination field onto the light modulator and the light modulator reflects the illumination field toward the imaging surface in one mode and reflects the illumination field away from the imaging surface in another mode. The modulator may, for example, include a Grating Light Valve (GLV) as sold by Silicon Light Machines of Sunnyvale, Calif., and the system may direct, via the imaging optics, either the zero order reflection or the first order reflection toward the imaging surface in various embodiments.
In particular, the image may be recorded from the zero order reflection 10 of the illumination field 12 from the modulator 14 at the imaging surface 16 as shown in FIG. 1A during imaging. As shown in FIG. 1B, when the modulator 14 is activated, the illumination field 12 is reflected at first order reflections 18A and 18B, and to a lesser extent at further order reflections (not shown). The first order reflections 18A and 18B are blocked from reaching the imaging surface 16 by energy absorbing blocking filters 20A and 20B. Imaging occurs, therefore, when the modulator 14 is not activated as shown in FIG. 1A. Ideally, no illumination should be directed along the path of the zero order reflection when the modulator 14 is activated as shown in FIG. 1B. In practice, however, it may be difficult to completely remove illumination from the zero order direction. The illumination field 12 and reflected fields 10, 18A and 18B may also be coplanar as long as the source is protected from the reflected signal, for example by using a directional blocking filter and a beam splitter.
Another conventional imaging system may employ an energy absorbing block filter 22 in the zero order direction 10 as shown in FIG. 2A, and a lens 24 to direct the first order reflections 18A and 18B toward the imaging surface 16 as shown in FIG. 2B. Such an imaging system, however, requires very precise alignment of the components to ensure that the first order reflections 18A and 18B converge at a common focal point at the imaging surface 16. Any mis-alignment of these components may significantly reduce image quality. Further, off-axis imaging limits the available depth of focus in the imaging system.
Also, many imaging systems employ an illumination field that is generally in the shape of a line of illumination, permitting a line of picture elements (or pixels) to be imaged simultaneously. The illumination fields 10, 12, 18A and 18B may, therefore, be in the shape of a line that extends a short distance along the modulator 14 and along the imaging surface 16 respectively. The use of an illumination field in the shape of a line may further complicate certain of the off-axis imaging constraints.
In certain applications it is desirable to provide an imaging system having a high contrast ratio that does not image when the power is not applied to the modulator, yet does not require highly precise alignment of numerous components and may be readily adjusted to optimum image quality.